The present invention relates generally to the control of LCD brightness for a portable computer and, more particularly, to a method and apparatus for conserving computer battery power by gradually reducing LCD brightness when the power supply is switched from the AC adapter to the battery.
Portable computers such as laptop or notebook computers typically draw power from one or more batteries or battery packs. One of the major shortcomings of the use of portable computers in a mobile setting, i.e., where there is no access to an AC power source, is the limited work time that may be obtained from the computer""s batteries. In order to maximize the work time that may be obtained from a battery charge, various power management or power conservation schemes have been implemented.
Portable computers typically have the capability to detect whether the computer is drawing power from an external power source, such as an AC adapter, or an internal battery power source. Since most power management techniques will affect computer performance, they are usually implemented when the computer is running on battery power. One such power conservation technique is to decrease the display brightness level when the computer is operating on batteries. It is also known to lower the central processing unit (CPU) operating speed when the computer is operating on batteries.
Other power management techniques may be employed regardless of whether the computer is using power from an AC adapter or batteries and involve turning off portions of the system after prespecified periods of nonuse. Such techniques include turning off or spinning down the hard disk drive after a prespecified period of nonuse; turning the display off after a prespecified period of nonuse; entering a low power sleep or standby mode (e.g., wherein the processor is temporarily shut down and the contents saved to memory after a prespecified period of nonuse); and turning off the entire system after a prespecified period of nonuse. The difference between AC adapter usage and battery usage in implementing the aforementioned power conservation techniques is that time periods are typically much shorter when the computer is operating on batteries.
Although nearly all of the aforementioned techniques increase the work time that may be obtained from the batteries, they do so at the expense of performance, for example, increasing user wait time when components that were turned off for power conservation are turned back on. Power management schemes which operate by decreasing LCD screen brightness when the computer is switched from AC power to battery power typically reduce brightness on the order of 50%. The reduction occurs when the AC adapter, or the power connection therefrom, is removed. In current systems applying a screen dimming feature, the user notices an immediate brightness reduction upon removal of the AC adapter. Of the various power saving techniques, reducing screen brightness has no effect on performance in terms of causing additional wait time, yet it is the most readily and immediately apparent to the user. Because screen brightness has heretofore been implemented by means of a sudden and marked change in screen brightness, a user may, upon noticing the decrease in brightness, manually increase the brightness or otherwise deactivate the feature, thus defeating the valuable power saving purpose of the display brightness reduction.
It would, therefore, be desirable to provide a display brightness control method and apparatus that eliminates any sudden drop in brightness. In accordance with the present invention, if the display brightness reduction is performed gradually so that it will be substantially unnoticeable to the user, the user will be less likely to manually increase display brightness when changing from an AC adapter power source to a battery power source.
In an embodiment, the present invention provides a display brightness control method and apparatus wherein screen brightness level reduction is performed sufficiently gradually so that the user does not notice a sudden brightness drop. In a preferred embodiment, the display brightness reduction is performed sufficiently gradually such that the brightness reduction is virtually unnoticeable to the human eye.
The display brightness control method and apparatus in accordance with this teaching may be implemented as a part of a power management system and method that optionally further includes additional power saving features.
The present invention employs a software or firmware routine that changes the display brightness level from a first brightness level to a second brightness level and that incorporates a limit in the rate of display brightness change over a period of time. The first brightness level will typically be a user selected brightness level or may be a default brightness level set when the computer is operating on AC power (hereinafter referred to as user selected brightness level). The second brightness level is a target brightness level which is deemed to power savings when the computer is operated on battery power, and may be a predetermined or fixed brightness level, a brightness level selected by the user for power savings, or may be defined as a brightness that is a certain percentage or brightness increment lower than the user selected brightness level. The time period over which the brightness reduction occurs is such that the brightness decrease does not appear as a sharp or sudden drop in brightness. In preferred embodiments, the time period is such that the drop in display brightness goes unnoticed or substantially unnoticed by the user. The time period over which the change in display brightness occurs may be any time period which would not cause a user to notice a sharp or sudden reduction in display brightness, and may be variable, for example, depending on the difference between the first and second brightness levels. The time period over which the brightness reduction occurs preferably ranges from about five seconds to a value on the order of tens of minutes, or longer. The time period more preferably ranges from about ten seconds to about twenty minutes or longer, and, most preferably, ranges from about ten seconds to about ten minutes. The target brightness level may be a fixed level or a level selectable by a user. The time period may also be variable, with larger time periods specified where larger changes in brightness level must be effected in order to reduce the display brightness from the user setting to the power saving target level, and the shorter time periods used where the change in brightness level is relatively small.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.